Mplayer for linux is a great movie player. MPlayer is well known for its wide format support and is known to support more multimedia formats than any other player. MPlayer easily plays MPEG/VOB, AVI, Ogg/OGM, VIVO, ASF/WMA/WMV, QT/MOV/MP4,RealMedia, Matroska, NUT, NuppelVideo, FLI, YUV4MPEG, FILM, RoQ, PVA files, supported by many native, XAnim, and Win32 DLLcodecs. With Mplayer, You can watch VideoCD, SVCD, DVD, 3ivx, DivX 3/4/5, WMV and even H.264 movies

xine is a free multimedia player. It plays back CDs, DVDs, and VCDs. It also decodes multimedia files like AVI, MOV, WMV, and MP3 from local disk drives, and displays multimedia streamed over the Internet. It interprets many of the most common multimedia formats available - and some of the most uncommon formats, too.

Kaffeine is another cool media player for KDE. Kaffeine supports multiple player engines while its default engine is Xine. Kaffeine can easily keep track of multiple play lists simultaneously and give you the ability to auto load subtitles files when playing a certain video giving Kaffeine a wide variety of supported media types and letting Kaffeine access CDs, DVDs, and network streams easily. With the latest updates, Kaffeine is able to play nearly every known audio and video format, however some may only be played with proprietary codecs. Kaffeine features include streaming, DVB, DVD, Video CD and CD audio.

VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols.
It can also be used as a server to stream in unicast or multicast in IPv4 or IPv6 on a high-bandwidth network.
It doesn't need any external codec or program to work.

Realplayer 11 for Linux is also something which a lot of people use to play more video, popular windows media files, real media filesand much more. With Realplayer you can create your personal playlists, control live streams and enjoy 5.1 surround sound (If you have good sound system)